Radiation generator having a conductive coating on a piezoelectric diffraction grating for varying the output frequency



. Sept. 5, 1967 J. E. YOUNG TOR HA ON A PIEZOELECTRIC DIFFRACT RADIATION GENERA VING A CONDUC'IIVE COATI ION GRA'IING FOR VARYING THE OUTPUT FREQUENCY Filed Dec. 28, 1964 FIG.

FIG. 2

INVENTOR JAM ES E. YOUNG ATTORNE Y3 tron stream. Since the or by varying the velocity of the electron as the adjustment of the cited United States Patent 3,340,416 RADIATION GENERATOR HAVING A CONDUC- TIVE COATING ON A PIEZOELECTRIC DIF- FRACTION GRATING FOR VARYING THE OUT- PUT FREQUENCY James E. Young, Pittsford, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Dec. 28, 1964, Ser. No. 421,557 7 Claims. (Cl. 315-4) This invention relates generally to high frequency electromagnetic wave generators, and particularly to generators of this type wherein such radiations are produced by interaction of an electron stream with an electromagnetic field.

The interaction of a stream of electrons with an electromagnetic field produced at the face of a periodic electrical structure is by now a well-known technique for generating and amplifying electromagnetic waves. Apparatus designed for such purposes are fully disclosed in a number of patents issued to Winfield W. Salisbury, and

. various modifications of such devices, particularly when adapted for production of radiation in the visible region, have in fact, become known as Salisbury Varotrons. De-

tails of the operation of such devices are dislosed in the Salisbury patents such as, for example, US. Patents Nos. 2,688,107, 2,634,372 and 2,866,917.

The present invention is basically an improvement upon the Salisbury Varotron and includes a modification of the design of the Salisbury devices whereby exceedingly rapid electrical control of the frequency output of erated is, in the general case, a function of the grating spacing, of the angle between the reflector plate and the grating plate, and of the velocity of the impinging elecgrating spacing is regarded as a fixed quantity, it becomes possible to vary the frequency output of the generators only in effect by adjusting the angular relationship between the reflector and the grating, stream. But, angular relationship is purely a mechanical operation, accuracy and speed of response are very slow when frequency modulation is accomplished in this manner. Furthermore, since the acceleration potentials for the electron stream are of the order T of several hundred kilovolts,

ready frequency control by this means is extremely diflicult.

It is accordingly the principal object of the present vention to provide modifications for high frequency electromagnetic wave generators of the Salisbury type 5 whereby rapid and readily controlled frequency modulation of the generator output may be achieved.

It is a further object of the present invention to provide super high-frequency electromagnetic wave generators having light frequency outputs over a broad and highly controllable frequency spectrum.

In accordance with the present invention it has been found that rapid and accurate variation of the frequency output of the type of generators alluded to may be accomplished by ruling the diffraction comprising a of a plate or grating upon a base piezoelectric ceramic material in the form strip, so that control of the grating spacing and thus of the generator frequency output, may be conveniently obtained by the mere application of electrical potentials between the faces of the piezoelectric plate.

The invention is illustrated by way of example in the following drawings, in which:

FIGURE 1 is an isometric and partially sectional view a generator incorporating the present improvement; FIGURE 2 is a diagrammatic cross-section of the essential elements, as shown in FIGURE 1;

FIGURE 3 is an enlarged cross-section of the diffraction grating utilized in the FIGURE 1 embodiment and illustrates the present improvement.

In FIGURE 1, an evacuated glass tube 1 encloses the principal elements of the present apparatus. The electron gun 2 is mounted at one end of this evacuated tube. The construction of such a gun is well known to those skilled in the art and includes the cathode element 17 which emits electrons which are then focused and accelerated by elements 18 and 19. While the latter elements are shown here as possessing circular geometry, it may in some instances be advisable to utilize the rectangular symmetry of the Pierce-type slot opening, so that the electron beam may be formed more nearly into a sheet. This would be the case where greater areas of interaction of the electron stream with the fields present at the grating is desired. In either case, the electron beam then passes through a set of vertical and horizontal deflection plates 3 and 4. Subsequently, the beam passes between the conductive metallic plate 8 and the metallized grating 6, and ultimately impinges upon the collector electrode 5. A variable output voltage source is provided at 11 with two conductive leads connected respectively to the top and bottom conductive surfaces of the metallized diffraction grating 6. A second variable output voltage source,

is provided at 12 with the output of this latter source connected between the top surface of the diffraction gratmg 6 and the conductive reflector plate 8. This ,.latter voltage source 12 by deflecting the beam toward or away from the grating surface makes possible 100 percent amplitude modulation of the output radiations. To accomplish such a function, the output of 12 will commonly include an A.C. component superimposed upon a steady D.C. level.

ductive metallic pate 8. The latter plate is essentially a polished metallic surface, the principal function of which is to coact with the diffraction grating 6 to reinforce standing electromagnetic waves present in the space between the two plates. 'As the electron stream passes in the vicinity of the periodic electrical structure comprising the uppermost face of the diffraction grating, traveling electromagnetic waves are produced. Interaction of I the electron stream with these traveling waves produces amplification of the waves, netic radiations pass from the tube envelope at the window 10.

In the present invention, the velocity of the electron stream is essentially constant. The stream preferably will have a potential of the order of several hundred kilovolts. In addition, the angular relationship ofthe reflecting plate and the coating diffraction grating is held constant. Modulation of the frequency output of the generator is obtained by selectively varying the grating spacing of the grating 6. This is accomplished by virtue of the unique structure of the grating, wherein the grating lines are ruled upon the face of a piezoelectric rectangular plate.

and the resulting electromag- The structure of the grating 6 is best shown in the enlarged sectional view of FIGURE 3. Here, 13 comprises a piezoelectric ceramic substance which may in a preferred embodiment be a thin, rectangular plate of lead zirconatelead titanate. Other piezoelectric materials such as barium titanate may also be utilized. The upper face of the plate is formed into a diffraction grating by a series of parallel rulings at points 7. It will be noted in FIGURE 3 that these rulings are such as to leave the sectional profile of the grating face as essentially a saw-tooth, and it has been found that such saw-tooth will desirably have a rise of the order of 10 degrees. In order to produce radiation in the visible spectrum, the grating spacing will desirably be of the order of 45,000 lines per inch.

The grating 6 carries on its top and bottom faces a thin, conductive, vapor-deposited layer of gold or other highly conductive metallic material. The two connections from the voltage source 11 are made respectively to these alternate conductive faces. Upon application of an electrical potential from source 11 across these two conductive faces, the plate contracts or expands along a direction perpendicular to the lines of the grating, so that an effective change in the grating spacing ensues. The change in the spacing in turn varies the frequency output of the generator. It has thus been found that voltage outputs from the source 11 in the range of 275-500 volts will normally be adequate to obtain from the generator, at least a frequency spread output in the range of 2,000-8,000 angstrom units.

While the present device has been described by way of an embodiment particularly suited for production of visible electromagnetic emanations, it will be obvious to those skilled in the art that the present apparatus may readily be modified for use at higher or lower frequency ranges; thus, for example, the production of electromagnetic emanations at modulated microwave frequencies is possible.

Having thus described the present invention it will become apparent that numerous modifications and departures as explained above may now be made by those skilled in the art, and yet such modifications and departures will fall within the scope of this invention. Consequently, the invention herein disclosed is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is:

1. A high frequency radiation generating apparatus comprising:

(a) a diffraction grating formed from parallel spaced lines ruled upon the face of a piezoelectric plate, said face carrying a conductive coating thereon;

(b) a conductive metallic plate positioned to reinforce standing electromagnetic waves in the space between said reflector and said diffraction grating;

(c) means to develop a beam of electrons and to direct said beam through said space;

(d) means to apply an electrical stress to said piezoelectric plate so that said plate will vary dimensionally in a direction perpendicular to said grating lines, and thereby change the spacing of said grating.

2. High frequency radiation generating apparatus comprising:

(a) a diffraction grating ruled upon the plane face of a piezoelectric plate, said plate being metallized upon said plane face and upon the plane face of said plate parallel and opposite to said face;

(b) a cooperating conductive metallic plate positioned to reinforce electromagnetic wave patterns in the space between said grating and said conductive metallic plate;

() means to develop a beam of electrons and project said beam through the said space between said grating and said conductive metallic plate to produce a high frequency radiation by the interaction between said beam and the electromagnetic field produced in said space;

((1) means to apply an electrical potential between the metallized faces of said plate bearing said grating so that the dimensions and thereby the spacing of said grating will vary in accordance with said electrical potential.

3. Apparatus according to claim 2 further including means to apply a controllable electrical potential between said conductive metallic plate and the adjacent metallized face of said piezoelectric plate, so that the electron beam in said space between said grating and said conductive metallic plate can be diverted, thereby achieving amplitude modulation of said electromagnetic radiations.

4. Apparatus according to claim 2 wherein the lines comprising said grating are ruled upon the face of said plate by a series of parallel cuts, the profile of which forms a saw-tooth pattern.

5. In a super high frequency generating apparatus including means to develop a beam of electrons, means including a diffraction grating to set up a standing electromagnetic wave pattern through which the beam passes to produce a high frequency radiation controlled by the interaction between the beam and said pattern, the im provement wherein said diffraction grating is formed from a series of parallel spaced lines ruled upon the metallized face of a piezoelectric plate, which plate bears a second metallized face opposite to said ruled face, and a controllable source of electrical potential is connected between said metallized faces so that the dimensions of said plate together with the spacing of said grating may be varied in accordance with said electrical potential, thereby modulating the frequency of said radiations in accordance with said electrical potential.

6. A high frequency electromagnetic wave generator comprising:

(a) an evacuated glass envelope;

(b) a metallized diffraction grating ruled upon the face of a piezoelectric ceramic plate, said plate having a plane metallized face opposite and parallel to said face, and said plate being supported and positioned within said glass envelope;

(c) a plane conductive surface positioned within said envelope parallel to the face of said plate bearing said grating lines with intervening space between said plate and said face;

((1) an electron gun positioned within said glass envelope to project a beam of electrons into said intervening space between said plate and said conductive surface so that high frequency electromagnetic radiations are produced by the interaction between said electron beam and traveling waves produced in said grating;

(e) a source of controllable electrical potential applied between the metallized faces of said plate so that an electrical stress may thereby be produced within said plate varying the dimensions of said plate in a direction perpendicular to the grating lines, thereby changing the spacing of said grating and thereby modulating the frequency of said electromagnetic radiations in accordance with said electrical potential.

7. Apparatus according to claim 6 further including means to apply an electrical potential between said conductive surface and the ruled face of said metallized plate so that said electron beam may be thereby deflected in the vicinity of said diffraction grating, thereby amplitude modulating the said electromagnetic radiations.

References Cited UNITED STATES PATENTS 3,259,014 7/1966 Johnson et a1. 88l45 

1. A HIGH FREQUENCY RADIATION GENERATING APPARATUS COMPRISING: (A) A DIFFRACTION GRATING FORMED FROM PARALLEL SPACED LINES RULED UPON THE FACE OF A PIEZOELECTRIC PLATE, SAID FACE CARRYING A CONDUCTIVE COATING THEREON; (B) A CONDUCTIVE METALLIC PLATE POSITIONED TO REINFORCE STANDING ELECTROMAGNETIC WAVES IN THE SPACE BETWEEN SAID REFLECTOR AND SAID DIFFRACTION GRATING; (C) MEANS TO DEVELOP A BEAM OF ELECTRONS AND TO DIRECT SAID BEAM THROUGH SAID SPACE; (D) MEANS TO APPLY AN ELECTRICAL STRESS TO SAID PIEZOELECTRIC PALTE SO THAT SAID PLATE WILL VARY DIMENSIONALLY IN A DIRECTION PERPENDICULAR TO SAID GRATING LINES, AND THEREBY CHANGE THE SPACING OF SAID GRATING. 